1. Field of the Invention
The present invention relates generally to the preparation and use of composite media for use in ion processing. More particularly, embodiments of the present invention relate to the preparation and use of ion processing elements that include composite media dispersed in a porous substrate.
2. Related Technology
Effective and efficient ion processing is an important consideration in numerous chemical and industrial processes. In general, ion processing refers to those processes, and/or devices which implement such processes, that are used to facilitate neutralization, removal, concentration, or other processing, of one or more ions present in a fluid stream, examples of which include industrial waste and process streams. One example of such a process concerns the removal of materials such as cesium, strontium, and/or uranium from an industrial waste stream prior to the discharge of the fluid stream into the environment.
While ion processing components and processes are often employed to remove undesirable constituents of a fluid volume or stream, such components and processes may also be used to collect and concentrate one or more desirable constituents of a fluid volume or stream so that those constituents can then be reserved for future use.
One area where ion processing techniques, materials, and devices are particularly useful is in the industrial environment. Typical industrial waste and process streams present at least two significant challenges to ion processing efforts. The first challenge relates to the flow rates of such industrial waste and process streams. Because industrial waste and process streams are often characterized by relatively high flow rates, the associated ion processing materials, systems, and components must be capable of admitting and processing the high flow rate waste and process streams without introducing an undue pressure drop or other resistance to flow that would tend to compromise the flow rate of those streams, and thereby slow down the overall rate at which ion processing occurs.
Another challenge that must be considered when implementing the treatment of industrial waste and process streams relates to the level of cleanliness that must be attained in the processed stream. In particular, the streams produced in industrial environments are often required to meet stringent standards with regard to the permissible concentration of various contaminants or other materials that are ultimately discharged into the environment. Thus, the treatment systems and devices must not only be able to handle relatively high fluid flow rates, but they must do so at a high level of efficiency.
Generally, the effectiveness and efficiency of a particular ion processing material is at least partially a function of the total surface area of the active component that contacts the material or fluid to be processed. The surface area, in turn, is a function of the porosity, or pore volume, of the ion processing material, so that relatively more porous ion processing materials typically possess a relatively greater surface area than relatively less porous ion processing materials. Thus, when considering two ion processing materials equivalent in all other regards, an ion processing material with a relatively larger surface area is capable of removing a relatively greater amount of contaminants or impurities from a fluid stream than an ion processing material with a relatively smaller surface area. In light of this relationship, a number of ion processing materials, systems, and devices have been devised with a view towards providing a relative increase in the surface area of the ion processing material so as to improve its effectiveness.
Various methods may be used to prepare ion processing materials so as to provide a relative increase in the surface area of the active component, of the ion processing material, that comes into contact with the fluid stream to be processed. In one case, the ion processing material takes the form of a composite medium that generally includes a supporting matrix and one or more active components dispersed within the matrix. Typically, the matrix comprises a plurality of small, slightly porous particles, sometimes referred to as beads. As suggested above, the overall surface area of the ion processing material that contacts the fluid stream simply comprises the sum of the surface areas of each of the individual beads which, in turn, is a function of pore volume.
In order to form the ion processing material, the matrix material is mixed with a particular active component selected for its ability to remove one or more predetermined constituents from the fluid stream. The ion processing material thus produced is typically disposed in a column through which the fluid stream to be processed is passed. Because the beads of the matrix material often assume a somewhat spherical shape, a plurality of spaces are cooperatively defined by adjacent beads. Accordingly, the fluid stream is able to flow through the ion processing material by working its way through the spaces between the individual beads.
While the slight porosity of some beads allows for a relatively greater ion processing area than would be possible if the beads were simply solid, such matrix materials have, as a result of their relatively small pore volume, proven rather ineffective in providing the performance required for effective and efficient processing of high volume fluid streams. Of course, the surface area of such ion processing materials can be increased somewhat by increasing the number of beads present in a particular column. However, there are practical limits to the attainment of very small bead sizes. Furthermore, while an increase in the number of beads produces a desirable overall increase in pore volume, and thus ion processing area, the increase represents a tradeoff with respect to the flow rate that a particular ion processing material can effectively accommodate.
In particular, as bead size is reduced, the size of the air spaces between adjacent beads is correspondingly reduced. Reduction in the size of the air spaces has at least one unfavorable consequence with respect to the flow of the fluid stream. Specifically, assuming a constant flow velocity, the volume of fluid that can flow through an opening is primarily a function of the size or area of that opening. This idea is generally expressed in the relationship Q=Va, where xe2x80x9cQxe2x80x9d is the volume of fluid flow per unit of time, xe2x80x9cVxe2x80x9d is the velocity of the fluid, and xe2x80x9caxe2x80x9d is the area through which the fluid passes.
In general then, where two volumes of ion processing materials in the form of respective composite media, equal in all other respects, have different numbers of beads, the volume of the ion processing material with relatively more beads defines a relatively smaller space through which the process stream can flow. In view of the aforementioned flow relationship, this means that the volume of ion processing material with a relatively greater number of beads is relatively more resistant to the flow of the process stream. Accordingly, in the case of an ion processing material comprised of very small particles, a powdered ion processing material for example, the resistance of the ion processing material to fluid flow is significant.
Thus, in the case of ion processing materials comprised of a composite medium employing a bead type matrix, the surface area of the ion processing material can be readily increased by increasing the number of beads. However, due to the inverse relationship, discussed above, between the air volume defined by the ion processing material and the ability of a given volume of the ion processing material to pass a predetermined flow, there are practical limits to the extent to which the surface area may usefully be increased.
As suggested earlier, another common ion processing material configuration is designed along the same general principles as those ion processing materials formed as composite media, but takes on a somewhat different form. In this particular configuration, no matrix is employed. Rather, a finely granulated or powdered active component is simply compressed under high pressure to form an ion processing material comprising a plurality of granules, or pellets, which are then disposed in a column for processing of a fluid stream.
While ion processing materials using compressed active component configurations typically have relatively large surface areas, they suffer from a variety of significant shortcomings. First, because the active component is initially in a powdered form, the flow of the fluid through a bed of granules of the active component of the ion processing material tends to wash away some of the active component, thus reducing the effectiveness and efficiency of the ion processing material over time. Another problem is that granules or pellets of the compressed active component tend to be rather brittle and can be easily broken and thereby rendered ineffective. Further, ion processing materials formed in this manner tend to crumble and fall apart over a period of time. Such ion processing material configurations are not well suited to withstand the rough handling and other conditions that may occur in many industrial environments.
Yet another shortcoming of compressed active component ion processing materials concerns the compression process that is used to form the granules or pellets of the compressed active component. In particular, large compressive forces are typically employed in order to ensure that the active component granules assume and retain the desired shape and size. However, the forces used to form the active component granules compress the active component so tightly that it is often the case that the fluid flow being processed never penetrates to the active component at the inner portion of the granules. Thus, the ion processing capacity of the active component in these types of ion processing materials is not fully utilized and much of the active component is essentially wasted. Such waste unnecessarily increases the amount, and thus the cost, of the ion processing material.
While the aforementioned shortcomings are of some concern in low volume ion processing applications such as might be encountered in a laboratory, these characteristics of ion processing materials that comprise compressed active component granules render such ion processing materials particularly unsuited for high volume applications such as are typically encountered in industrial environments.
In environmental applications, for example, it is often the case that large volumes of fluid, in some cases as much as 100 to 400 gallons, must be sampled so that analyses of the sample will provide accurate and scientifically valid results. Types of fluids typically sampled include, but are not limited to, ocean water, groundwater, water from inland waterways such as lakes and rivers, landfill runoff, and the like.
Because of the inability of known ion processing media, devices, and systems to readily process large volumes of fluids, personnel sampling these fluids are often compelled to collect the sample required and transport the sample back to a processing facility for analysis. Transportation of such large samples can be problematic in many cases, especially where the sample is gathered in a location remote from the laboratory or facility where the sample is to be analyzed. In particular, transportation of large samples from remote locations is both time-consuming and expensive.
A related problem concerns processing of large samples once they finally reach the processing facility. Typically, such samples must be evaporated and/or otherwise treated by processes comprising numerous steps so that the constituents of those samples can be concentrated and analyzed. Such extensive processing is undesirable, at least because it is time-consuming, expensive, and often requires special equipment.
In view of the foregoing problems and shortcomings with existing ion processing materials and systems, it would be an advancement in the art to provide an ion processing element comprising a large surface area composite medium disposed in a porous substrate which offers relatively little resistance to fluid flow, wherein the composite medium comprises one or more active components uniformly dispersed in a matrix material having a relatively high surface area so as to facilitate relatively high rates of ion processing.
The present invention has been developed in response to the current state of the art, and in particular, in response to these and other problems and needs that have not been fully or adequately addressed by currently available ion processing materials and elements.
Briefly summarized, embodiments of the invention are directed to an ion processing element comprising a composite medium dispersed in a highly porous substrate. The composite medium includes a large surface area matrix material within which one or more active components are disposed. Embodiments of the invention are particularly well suited for use in high volume applications requiring effective and efficient removal, or other processing, of actinides such as uranium (U), plutonium (Pu), and americium (Am), lanthanides such as europium (Eu) and cerium (Ce), alkali metals such as cesium (Cs), alkaline earth metals such as strontium (Sr), organic contaminants, and chlorine, such as from water that is to be used for human consumption. In general however, embodiments of the invention are effective in any application where efficient and effective ion processing of high volume flows is required.
Note that, as used herein, xe2x80x9cactinidesxe2x80x9d include any and all elements of the Actinide Series as depicted by the periodic chart of the elements, as well as any and all compounds substantially comprising an element of the Actinide Series. Similarly, xe2x80x9clanthanidesxe2x80x9d refer to any and all elements of the Lanthanide Series as depicted by the periodic chart of the elements, as well as any and all compounds substantially comprising an element of the Lanthanide Series.
Embodiments of ion processing elements include a porous substrate, preferably comprising fibrous glass, impregnated with a composite medium. The composite medium, in turn, comprises an active component supported by a porous matrix material. The matrix material, in some embodiments, is substantially comprised of an organic polymer, such as polyacrylonitrile (PAN). One or more active components, such as crystalline silicotitanate (CST), carbon, or octyl (phenyl) N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) for example, are dispersed throughout the matrix material.
In one embodiment of the invention, the composite medium is prepared by first dissolving a desired amount of PAN in a solvent, nitric acid (HNO3) for example, so as to produce a matrix solution of a desired concentration. One or more active components are then mixed with the matrix solution to produce a composite medium solution (CMS), which may comprise a suspension, emulsion, solution, or other form. Preferably, both the dissolution of the PAN and the mixing of the active component(s) with the matrix solution are performed at room temperature and pressure.
A pressure differential is then established across the porous substrate, and the CMS is introduced on the high pressure side of the pressure differential. The pressure differential causes the CMS to flow into, and substantially impregnate, the porous substrate. The CMS impregnated substrate is then immersed in a water bath so as to facilitate substantial dilution of the nitric acid the CMS. Such dilution of the solvent desirably causes the composite medium to solidify in the substrate. After the solvent has been substantially diluted, or otherwise neutralized, the ion processing element is then dried and ready for use.
In operation, a fluid stream is passed through the ion processing element and the composite media disposed therein removes one or more constituents of the fluid stream. By virtue of their porosity, the substrate and the matrix material possess a large pore volume which, as previously discussed, translates to a large surface area for ion processing. Thus, the active component dispersed throughout the matrix possesses a high ion processing capacity with respect to the fluid stream in contact therewith.
Another desirable consequence of the porosity of the substrate is that the substrate offers relatively little resistance to flow through the ion processing element, and thus the kinetic properties of the ion processing element are favorable. That is, the porosity of the substrate in which the composite media are deposited facilitates accommodation of a high volume fluid stream without imposing a material drop in pressure of the fluid stream that would otherwise compromise processing rates. Further, the portability of the ion processing element makes it well-suited for use in off-site processing of fluids. Finally, because the matrix material is relatively durable, it is well suited to withstand the rough handling and environmental conditions typically encountered in industrial applications and other uses.
These and other features and advantages of the present invention will become more fully apparent from the following description and appended claims.